Vehicle designers today are challenged by many requirements of both design and performance. One of the most important requirements, and often one of the most difficult to achieve, is directed to the management and reduction of noise, vibration and harshness, or NVH.
An area of particular concern is the transmission of vehicle vibrations to the vehicle seats, a problem that is most pronounced in the operation of trucks and off-road vehicles. The problem is also more apparent in heavier seats having greater mass due to a higher component content (such as, but not limited to, power lumbar mechanisms, climate controlled seats, multi-way power tracks, and power recline mechanisms).
Unoccupied passenger seats are most vulnerable to vibration. Without the mass of an occupant available for dampening, the unoccupied passenger seat may be shaken, thus causing a visible motion in the seat. The driver may notice this movement and may be annoyed or distracted by the seat motion. A shaking seat may also generate an audible noise, such noise also being an annoyance or distraction to the driver and other vehicle occupants.
Attempts have been made to reduce the amount of vibration introduced to the seat with varying degrees of success. One general effort is directed to increasing the stiffness of the seat. While reducing vibration this approach sacrifices occupant comfort and may result in poor performance in a rear-impact event.
Another attempt at reducing seat vibration relies on mass tuned damper technology. A tuned mass damper is also known as a harmonic absorber or an active mass damper designed to stabilize against harmonic vibration. The tuned mass damper may be any of a variety of devices with the common goal of reducing the amplitude of mechanical vibrations.
Particularly, as applied to the vehicle seat, a mass tuned damper is incorporated into the seat back, typically but not exclusively in the passenger seat back, to dampen vibrations transmitted to the seat back. This approach relies on a rubber coated mass tuned damper.
While offering certain improvements this approach also suffers from certain disadvantages. One disadvantage is production cost. The current mass tuned damper is an overmolded rubber steel mass attached to the seat back frame. Costs related to overmolding and to the requisite hand trimming of flash are high. In addition, to be effective at reducing or eliminating vibration the mass tuned damper needs to be tuned to the frequency of the seat. This also adds expense to the production and use of this element.
Known rubber coated mass tuned dampers tend to be heavy and thus add undesirably to the overall weight of the vehicle. Additional vehicle weight runs contrary to the goal of vehicle weight reduction for the sake of improved fuel economy.
Another disadvantage related to the use of the mass tuned damper has to do with space restrictions. The rubber coated mass tuned damper has limited range of fore/aft motion and lateral motion before contacting the seatback frame. Particularly, when the rubber coated mass contacts the back frame it generates an audible thumping sound when the vehicle is driven over a rough area, such as a railroad track or a speed bump. Because of inherent spaced restrictions little improvement related to reduction or elimination of the thumping sound can be expected through the use of current technology
Accordingly, as in many areas of vehicle technology room for improvement remains in the art of dampening of vehicle seat vibration.